BMW 1989-1995 525i Service Manual page 206

170-2
RADIATOR AND COOLING SYSTEM
Warnings and Cautions
The following warnings and cautions should be observed
when working on the cooling system .
WARNING -
• At normal operating temperature the cooling sys -
tem is pressurized. Allow the system to cool as
long as possible belore opening-a minimum of
an hour-then release the cap slowly to aI/ow
safe release 01pressure.
• Releasing the cooling system pressure lowers
the coolant s boiling point and the coolant may
boil sucaemy. Use heavy gloves and wear eye
and face protection to guard against scalding.
• Use extreme care when draining and disposing
of engine coolant. Coolant is poisonous and le-
thal to humans and pets. Pets are attracted to
coolant because of its sweet smell and taste.
Consult
a
veterinarian immediately if coolant is
inges ted by an
animal.
CAUTlON-
• Avoid adding cold water to the coolant while the
engine is hot or overheated. If it is necessary to
add coolant to
a
hot system. do so only with the
engine running and coolant pump turning.
• Disconnecting the battery cables may erase lault
codes stored in control unit memory. Check a nd
record any fault codes belore oisconnectinq bat-
tery.
TROUBLESHOOTING
Most cooling system faults can be grouped into one of three
categories: 1) cooling system leaks. 2) poor coolant circula-
tion. or 3) radiator cooling fan faults .
When investigating the cause of overheating or coolant
loss. begin with a visual inspection. Be sure to check the con-
dition and tightness of the coolant pump drive belt. Check hos-
es for cracks or softness . Check clamps for looseness. Check
the coolant level and check for evidence of coolant leaks from
the engine.
Check that the radiator fins are not blocked with dirt or de -
bris. Clean the radiator using low-pressure water or com -
pressed air. Blow outward. from the engine side out.
Inspect the coolant pump by first removing the drive belt
from the pump. Firmly grasp opposite sides of the pulley and
check for play in all directions. Rotate the pulley and check
that the shaft runs smoothly.
TROUBLESHOOTING
NOTE-
The coolant provides some lubrication for the pump
shaft. so an occasional drop of coolant leaking from the
pump is acceptable. If coolant drips steadily from the
vent hole. Ihe pump should be replaced.
The cooling system becomes pressurized at normal operat-
ing temperature . which raises the boiling point of the coolant.
Leaks may prevent the system from becoming pressurized.
allowing the coolant to boil at a lower tempe rature . If visual ev-
idence is inconclusive. a cooling system pressure test may
help to pinpoint hard-to-find leaks.
If the cooling system is full of coolant and holds pressure.
the next most probable cause of overheating is the result of
poor coolant circulation due to a loose or worn drive belt. a
failed thermostat or coolant pump . a pinched or restricted
hose. or a partially clogged radiator.
Pressure Test
A cooling system pressure test is used to check for internal
leaks. Some of the common sources of internal leaks are a
faulty cylinder head gasket. a cracked cylinder head . or a
cracked cylinder block.
To do a cooling system pressure test. a special pressu re
tester is needed . The engine should be fully warm when mak-
ing the test.
WARNING-
At normal operating temperature the cooling sys-
tem is pressurized. Allow the system 10 cool before
opening. Then release the cap slowly to allow safe
release of pressure.
With the engine cold. install a pressure tester to the expan-
sion tank. Allow the engine to reach operating temperature.
then pressurize the system to the specification listed below.
Pressure should not drop noticeably for at least 2 minutes. If the
pressure drops rapidly and there is no sign of an external leak.
the cylinder head gasket may be faulty. Consider a compres -
sion or leak down test. as described in 100 Eng ine-General.
Cooling system test pressure
• Maximum 1.0 bar (14.5 psi)
CAUTlON-
Exceeding the specified test pressure could dam-
age the radiator or other cooling system compo-
nents.
NOTE-
The screw-on Iype expansion tank cap should also be
tesled using
a
pressure tester and the correct adapter.
Carefully inspect the cap for damage. A laulty cap or
a
damaged cap gasket should be replaced.